Archive for the ‘Deforestation’ Category

Here is an update of review of the best papers on climate science in the past year. If you want a broader overview of the literature in the past few years, focusing specifically on how unrestricted emissions of greenhouse gas emissions are projected to impact the United States, try “An introduction to global warming impacts: Hell and High Water.”

In 2009, the scientific literature caught up with what top climate scientists have been saying privately for a few years now:

Many of the predicted impacts of human-caused climate change are occurring much faster than anybody expected — particularly ice melt, everywhere you look on the planet.

If we stay anywhere near our current emissions path, we are facing incalculable catastrophes by century’s end, including rapid sea level rise, massive wildfires, widespread Dust-Bowlification, large oceanic dead zones, and 9°F warming — much of which could be all but irreversible for centuries. And that’s not the worst-case scenario!

The consequences for human health and well being would be extreme.

That’s no surprise to anybody who has talked to leading climate scientists in recent years, read my book Hell and High Water (or a number of other books), or followed this blog. Still, it is a scientific reality that I don’t think more than 2 people in 100 fully grasp, so I’m going to review here the past year in climate science. I’ll focus primarily on the peer-reviewed literature, but also look at some major summary reports.

Let’s start with the basics. Heat-trapping greenhouse gases are at unprecedented levels, and the paleoclimate record suggests that even slightly higher levels are untenable:

Since we have record levels of heat-trapping gases, it’s not surprising that we also learned that this was the hottest decade in the temperature record and that the Arctic is the hottest in at least two millenia.

In two key papers, we learned that the planet is warming from those GHGs just where climate science said it would — the oceans, which is where more than 90% of the warming was projected to end up (see “Skeptical Science explains how we know global warming is happening.“). The key findings in the second study are summed up in this figure:

Using the first “fully interactive climate system model” applied to study permafrost, the researchers found that if we tried to stabilize CO2 concentrations in the air at 550 ppm, permafrost would plummet from over 4 million square miles today to 1.5 million. If concentrations hit 690 ppm, permafrost would shrink to just 800,000 square miles:

“This graph shows the percentage increase in area burned by wildfires, from the present-day to the 2050s, as calculated by the model of Spracklen et al. [2009] for the May-October fire season. The model follows a scenario of moderately increasing emissions of greenhouse gas emissions and leads to average global warming of 1.6 degrees Celsius (3 degrees Fahrenheit) by 2050. Warmer temperatures can dry out underbrush, leading to more serious conflagrations in the future climate.”

And the plausible worst-case scenario is even worse than this grim “business as usual” emissions case:

This is the “plausible worst case scenario” for 2060 from the UK Met Office that occurs in 10% of model runs of high emissions with the carbon cycle feedbacks [temperature in degrees Celsius, multiple by 1.8 for Fahrenheit]:

Measurements of atmospheric CH4 from air samples collected weekly at 46 remote surface sites show that, after a decade of near-zero growth, globally averaged atmospheric methane increased during 2007 and 2008. During 2007, CH4 increased by 8.3 ± 0.6 ppb. CH4 mole fractions averaged over polar northern latitudes and the Southern Hemisphere increased more than other zonally averaged regions. In 2008, globally averaged CH4 increased by 4.4 ± 0.6 ppb; the largest increase was in the tropics, while polar northern latitudes did not increase. Satellite and in situ CO observations suggest only a minor contribution to increased CH4 from biomass burning. The most likely drivers of the CH4 anomalies observed during 2007 and 2008 are anomalously high temperatures in the Arctic and greater than average precipitation in the tropics. Near-zero CH4 growth in the Arctic during 2008 suggests we have not yet activated strong climate feedbacks from permafrost and CH4 hydrates.

The anti-science crowd use smoke and mirrors to distract as many people as possible, but the rest of us need to listen to the science and keep our eyes on the prize — reversing greenhouse gas emissions trends as quickly and rapidly as possible.

Amid questions over the Amazon forests’ capacity to survive climate change, a renowned tropical biologist says that in fact the fears are real, reports Tierramerica.

Speaking at the Biodiversity Science Policy Conference in Paris, Thomas Lovejoy, biodiversity chair at the Washington DC-based Heinz Center for Science, Economics and the Environment, and chief biodiversity adviser to the president of the World Bank, described the Amazon rainforest as “very close to a tipping point”.

The triple combination of rampant deforestation, fires, and rising temperatures could devastate the rainforest ecosystem within 65 years, explained Lovejoy, shrinking the Amazon rainforest to one-third of its original size. Such a contraction would result in countless extinctions, losses in vital freshwater sources, a decline in regional rainfall, and the weakening of one of the world’s most important carbon sinks.

Patchwork of legal forest reserves, pasture, and soy farms in the Brazilian Amazon. Photo by Rhett A Butler.

Lovejoy’s assessment is in line with the Intergovernmental Panel on Climate Change’s (IPCC), which warned that climate change could produce a drier Amazon, resulting in a 40 percent loss of the ecosystem. The IPCC has recently come under criticism for this assessment, yet despite sloppy citations (the IPCC cited a WWF report rather than scientific studies) the organization’s statement is in line with a number of tropical ecology studies.

Lovejoy told Tierramerica that the “tipping point for the Amazon is 20 percent deforestation” based on a report by the World Bank entitled, Assessment of the Risk of Amazon Dieback. At this point deforestation combined with spreading fires and overall warming of 2 degrees Celsius would cause parts of the Amazon’s hydrogeologic system to break down.

Since the Amazon rainforest creates at least half the rainfall needed to sustain itself, the loss of forest cover and general drying would create a feedback cycle whereby large areas of the forest would revert to savannah. This process would release tens of billions of additional carbon into the atmosphere.

The threshold of 20 percent is close: already 17 to 18 percent of the Amazon has been lost. However, other studies have found that ‘die-off’ point for the Amazon rainforest would occur only after 40-60 percent of the forest was lost. The differences in such findings displays the complicated nature of climate science, however the studies all agree that the Amazon faces unparalleled pressures that if unchecked will result in massive forest loss.

Deforestation in the Brazilian Amazon. Photo by Rhett A Butler.

The strength of the World Bank report is that it does not focus solely on deforestation or climate change, but on the synergistic effects of deforestation, warmer temperatures, and fires.

Another tropical forest expert, Simon Lewis of Leeds University, told the BBC that while the IPCC citation of WWF was bizarre, the IPCC findings were hardly incorrect.

“It is very well known that in Amazonia, tropical forests exist when there is more than about 1.5 meters of rain a year, below that the system tends to ‘flip’ to savannah,” he explained. “Indeed, some leading models of future climate change impacts show a die-off of more than 40 percent Amazon forests, due to projected decreases in rainfall.”